1. Field of Invention
This invention relates to a method and apparatus for controlling the pressurized ink to an ink jet printing head so that the print head is sealed off full of ink during non-printing periods.
2. Description of Prior Art
There has been known in the prior art pressurized ink jet systems. In the binary type pressurized ink jet system described in U.S. Pat. No. 3,373,437 to Sweet et al, a plurality of jets is provided in one or more rows. The jets are broken up into a series of uniform ink drops which are selectively charged at drop breakoff with a single charge amplitude so that the charged drops are deflected by a constant field to an ink drop gutter. The uncharged ink drops continue along the original jet stream paths to impact the recording medium. A visible human-readable record can be formed in this manner by leaving uncharged those drops required for printing during relative print head-to-recording medium motion.
To meet the present resolution requirements for computer systems printing applications, it is a requirement of the multi-jet binary systems for the jets to be closely spaced and to produce a small diameter mark on the recording medium. The resolution requirements dictate the use of very small nozzle openings, and, as the nozzle openings become smaller, the nozzles become more vulnerable to clogging. Prior art systems provided some control over the ink supply system and the sequencing of operations for startup, operation and shutoff of the pressurized ink systems. However, these systems have not always been successful in preventing entrance of contaminant material into the ink system which may result in clogged nozzles and unacceptably poor print quality.